Electronic Structure of LK-99

That domain knowledge wouldn't have suggested exploring this space for superconductivity.

Turn the material science problem around: instead of looking for a substance that has a specific property, look at many substances until small amounts of any interesting property (young's modulus, etc) show up. By looking for "anything interesting" you are more likely to find something of interesting (ideally, several somethings). And then you also know a starting place to begin optimiziation.

(I'm not saying these things out of ignorance; this technique has worked well for me at times when I had exceptionally large amounts of CPU available to me, and it's also worked well in the drug industry, which has similar problems to material science.)

I'd probably approach 90% confidence with ~2-3 different measurements from different labs showing similar stories. Select from the grab bag of possible experiments that could all collaborate and provide consistency in their stories: specifically things like measuring the critical current, critical magnetic field, high quality electrical resistance in various ways (lots of transport), STM measurements of gaps, ARPES measurements of gaps, XRD showing crystal structures are what we expect that matches the DFT, a study on the domain sizes/effects (since this is relying on a substition at the right place, necessarily I suspect that there will be domain effects / "doping" style things... so how those play out in terms of purity and quality of results will be interesting). There will be a lot to study and characterize, and every extra measurement that is consistent rapidly increases that confidence. I'd say I'd get to "100%" (as close as someone could be) after ~10-20 papers across many different labs and measurements. I'd hope we'd get there in ~3-6 months.

What I'm actually even slightly more excited about is "what comes next" -- not the market part, but the "fast follow science". For instance, in the few years after LCBO and LSCO were found (TC~30K) we quickly found YBCO and BSCCO (Tc~130K). I would expect that we'll find a whole class of these materials with substitution tricks that possibly work, and there will be a whole slew of options for "going to market" with the technology. The door this opens is what is more exciting than the specifics of LK-99 itself in my opinion.

Estimating times, after the fast follow science (0.5-2 years optimistically?) we will hopefully have the actual "we're all convinced this is real, and the technology can start to be applied in real devices". Specifically, after everyone is pretty clear on a lot of the material properties and ways to reproducibly make high-quality crystals, so consistency is clear on measurements... then begins the cycles on how to manufacture high enough quality material at scale that it can actually be applied. (specifically, these materials (assuming they're like YCBO/BSCCO) are superconducting crystals that have grains, alignment issues, are physically brittle, have homogeneity issues, etc.) While each solvable, these are all real engineering and material challenges that increase cost to manufacture, and all of this will probably take time before we suddenly get wide-scale products that use this (this is all assuming it's real, haha, there's still plenty of reason to be skeptical).

Same with me, it gives me the same feeling of "Living in a science fiction world" that I once felt when cell phones or Google maps came out.

Of course even tough I still use both profusely every day, the feeling of novelty wore out. I expect the same will happen with this.

>Assuming this is all true, why is it just now coming to light? Did they just not know what they had?

This is why the calculations by Sinéad Griffin looked so interesting to me: they suggest that the superconductivity depends on an unconventional substitution pattern that might not (in fact should not) occur in most samples of Cu-doped lead apatite. So the active structure was only present in tiny quantities, requiring a long period of trial-and-error optimization.

Again, this is far from proof, but I thought it was at least very curious to have some theory that explains not just a mechanism for superconductivity but also why the samples seem to teeter on the edge of superconductivity so frustratingly.

The replies to my previous post ( https://news.ycombinator.com/item?id=36958419 ) suggesting that flat bands appear simply because copper doesn't belong in that lattice seem inconsistent with the fact that a flat band was not observed when copper substituted at the wrong type of lattice site. If flat bands appear merely because of the unpaired copper electron, they should appear when it is substituted only at Pb {2} sites, but they don't. The appearance of this band structure plus the observance of diamagnetism just takes us from happenstance to coincidence, so we need one more to conclude it is enemy action.

FWIW I don't work in condensed matter physics but I have taken the classes at grad level a few years back. I also should really be doing other things, but this is probably the most fun scientific news cycle since 'Oumuamua at least. (COVID doesn't count as "fun".)

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